1. Field of the Invention
The present invention relates to a cross-coil type indicating instrument which has a magnet arranged in a plurality of coils that are wound mutually crossed, and indicates the value of a detected physical quantity such as temperature by means of the rotation of the magnet caused by the electrical signal that corresponds to the sensor output supplied to the coils.
2. Description of Prior Art
The cross-coil type indicating instrument is being used, for example, as the water temperature meter of motor vehicles.
In the water temperature meter, a permanent magnet which acts as the pointer is provided in a plurality of coils that are wound mutually crossed. The electrical current which corresponds to the output of the temperature sensor is supplied to the coils to rotate the permanent magnet. In operation, when the water temperature is raised from a low temperature, a current that corresponds to the water temperature is supplied to each of the coils, and the permanent magnet is rotated to indicate the water temperature. Then, when the water temperature reaches the steady-state temperature for normal driving of the motor vehicle, for instance, 82.degree. C. to 110.degree. C. or so, the electrical signal to each of the coils become constant, and so becomes the indication angle of the pointer.
However, when the water temperature goes up further, the electrical signal that is supplied to each of the coils is changed again, and the pointer is rotated further in the same direction to indicate the corresponding higher temperature. Consequently, according to the present water temperature meter, it is arranged that the water temperature is displayed if it is too low or too high; and it is arranged that the pointer will not show fluctuations due to minor ups and downs of the water temperature at the steady-state driving temperature. Therefore, during a normal driving of the motor vehicle, it is unnecessary to worry about the conditions of the water temperature.
However, in such a system, the control circuit for controlling the supply of the current to each of the coils has an elementary configuration. Consequently, the range of the temperature for normal driving is susceptible to easy variation due to the dispersion in the characteristic properties of the circuit elements used, so that a problem with the system arose in that the desired indication precision was not realized.